If you want to head up your own faction then you will want to have a butt load of money saved up. Get a strong force and go capture a City/Castle. Its best if it already has a commander, but not necessary. Stick all your troops in the castle then go recruiting. Grab from the Town Commander, villages you own, taverns, and mercenary camps.
Might as well put some money into an improvement or two while you're at it, but that isn't necessary. Different commanders give access to additional troops in town.
Once your party is full go back to your city/castle and stuff it full of troops. Rinse/Repeat until you have ~300 troops sitting in the garrison and a party large enough to go capture another city/castle. Continue capturing and building forces (don't need 300 in all, 100 will do fine in most - 300 is just a reserve so that you can quickly garrison a new city). I usually do this for a while until I have 4 or 5 cities/castles close to each other, then I build up a force of high level cavalry and go hunting for lords. Also, this is usually the point where I get bored and reroll my character to something new lol.
